PDF files are blank or cause an error message on Mac

When you install or update Adobe Reader, it installs the "Adobe Acrobat NPAPI Plug-in" for viewing PDF files inside your browser. The problem is that this plugin does not work in Firefox. The PDF file may be blank or you may see the message, Adobe Reader cannot show documents in this browser. We'll explain how to fix that.

On the menu bar, click on the Firefox menu and select Preferences….Click the menu button
and select Preferences….

Select the Applications panel.

Type pdf into the search bar.

For each content type listed, click on the drop-down menu in the Action column and change the selection to use (if available) Preview in Firefox, Preview, Adobe Reader, or PDF Browser Plugin (if you are using the Schubert PDF plugin).